The hydraulic system of a deck winch has been drained, flushed, and refilled with hydraulic fluid. An erratic knocking noise from the hydraulic motor when the winch is started would indicate __________.

Correct Answer: Option C — air trapped in the system

Erratic knocking in a hydraulic motor following maintenance is a classic symptom of air trapped in the system. Air bubbles compress and expand under pressure, causing cavitation and mechanical shock. The system must be properly bled or purged of air to restore smooth, quiet, and efficient operation.